Long term leaching of stabilised wood ash

Abstract

The long-term leaching of two wood ashes, a granulated ash from a circulating fluidized bed boiler (CFB) and a grate-fired boiler (GF) ash, stabilized by wetting and agglomeration, was simulated in laboratory experiments and theoretically, with a kinetic model. Ash particles extracted from forest soil 2 yrs after spreading were also analysed. The results showed that leaching rates for nutrients depend on particle size, durability of ash aggregates and nutrient speciation. The hard CFB ash granules released less of their salt content than did the more fragile GF ash aggregates. Differences in matrix durability as well as in Ca speciation also rendered the CFB ash granules the lowest Ca leaching rates. The Ca leaching rates predicted for different particle sizes by the kinetic model were significantly higher than those obtained experimentally. This discrepancy is probably due to factors such as decreasing porosity and chemical inhibition of calcite dissolution during experiments 26 refs, 6 figs, 7 tabs